Method of adding lead to steel



Oct. 7, 1958 c. R. FUNK ETAL METHOD OF ADDING LEAD TO STEEL Filed April 7, 1955 l ime:

w \\\\\\\\\\\\\\\QQE CHARLES R. FUNK RIGHARD M. BARNHART INVENTQR.

ATTORNEY METHOD OF ADDING LEAD TO STEEL Charles R. Funk, Latrobe, and Richard M. Barnhart,

Legonier, Pa., assignors to Alco Products, Inc., New

York, N. Y., a corporation of New York Application April 7, 1955, Serial No. 499,802

4 Claims. (Cl. 22-200) This invention relates to a method of adding lead to steel.

It has long been known that the inclusion of certain amounts of lead in steel considerably improves the machinability of the steel. The most desirable mixture of lead and steel for such purposes requires that the lead be evenly dispersed in the steel in submicroscopic form. Various methods have been used in an attempt to produce such a mixture but none have accomplished a satisfactorily uniform dispersal of the lead throughout the ingot, particularly in the case of larger sized ingots or ingots of high quality application. It is, therefore, the object of this invention to provide a method of adding lead to steel in such a manner that the lead is uniformly dispersed in the steel in the finished product.

It has been attempted, for example, to mix the lead directly into a bath of molten steel during tap into the ladle. It has been found in such practice, however, that a large porportion of the lead settles directly to the bottom of the bath and only a small amount of the lead is dispersed through the bath. Such lead as may be dispersed in the bath is not of sufiicient quantity to be of any value when later poured from the ladle into the mold. Furthermore, the dispersed portion tends to become agglomerated during solidification in the mold. Steel ingots formed from such a bath would have no commercial value.

Another method attempted has been to introduce the lead on top of the metal in the mold; but this has likewise proved unsatisfactory. Even though the lead is finely divided, it collects in large masses and sinks to the bottom of the mold without effective dispersal. Moreover, a substantial portion of the lead is oxidized forming large volumes of dangerous fumes containing lead oxide.

Another method resorted to has been to introduce the lead directly into the descending column of molten steel as it is poured from the ladle into the mold in top pouring practice. Irregular and inconsistant lead recovery, excessive fuming, and heavy segregation of lead in the ingot, particularly in its lower portion, results from this method. This method is further objectionable since it has been found necessary to take an extra discard from the bottom of the ingot, preferably after the ingot has been forged or rolled into a bloom or billet. Even after this second discard is taken, tests are required to determine the quality of the remainder of the bloom or billet and a further discard may have to be taken. Blooms or billets made from top-poured ingots have been satisfactory for small sections or for medium or commercial quality products such as use only free cutting, free machining, or screw stock but are unsatisfactory for high quality applications or for heavy sections such as are provided for the fabrication of large pinions, gear rings, or sections used in high pressure vessels.

In top pouring practice, the molds are filled with great rapidity by the pouring of steel from the ladle directly into the top of the mold. Such rapid pouring introduces States Patent C 28 54571 6 Patented Oct. 7, 1958 the steel into the mold in a tremendous super heat which must be dissipated through the mold walls before solidification can take place. The metal remains molten in the mold in various states of sluggishness for relatively a long period of time. A thin shell first forms on the ingot and the solidification develops gradually inwardly from the shell. Lead mixed with the steel in the inner portion of the cooling ingot thus has the opportunity to segregate and migrate downward through the still molten steel. From the foregoing, it is apparent that the larger the ingot and the greater the cross section, the greater will be the segregation and migration. In fact, present prac tice has shown some moderate degree of successful mixing only in ingots up to approximately 27 inches cross section.

It should further be pointed out that in top pouring practice, the greatest degree of success has occurred with fast pour and hotsteel. But certain grades of steel, for various reasons known to those in the art of steel making, cannot be poured fast or hot; and in such cases, the slow rate of fill prevents satisfactory lead recovery.

Still another objectionable feature of top pouring practice is that large amounts of fumes containing toxic lead oxide are generated, the elimination of which requires elaborate and expensive venting equipment.

We have found that if the lead'is properly introduced into the descending column of molten steel or into the pool or reservoir of steel formed at the bottom in the center runner in the bottom pouring method of molding, the objectionable features of top pouring practice are eliminated and a satisfactory mixing is obtained for all sizes and quality of ingots. A considerable advantage of bottom pouring is that heat is permitted to escape at a high and desirable rate; hence the troublesome super heat factor in top pouring practice is diminished.

In the drawing there is shown in cross section the apparatus for performing the method of this invention.

, To achieve a proper introduction of the lead into the steel by the method of the invention, we have provided conventional bottom pouring molding equipment in which a vertical center runner 10 having a passage 11 of relatively small diameter communicates with a plurality of sprues 12 from the bottom of the center runner to the molds 13 (only two of which are shown). Steel is initially poured from the ladle 14 into the center runner 11 and its flow is so controlled that the bottom of the center runner fills up sufficiently to form a pool or reservoir, as indicated in the drawing. The diameter of the center runner passage should of course be great enough to permit pouring at a rate sufiicient to supply the sprues and also to create a pool of metal in the bottom of the runner. A feeder pipe 15 connected to a source of lead (not shown), which may be in either liquid form or in the form of shots or pellets, is disposed so that its supply end 16 is located adjacent the descending column of steel. The pipe end is directed so that the lead drops down the runner passage into the pool where effective mixing takes place. As heretofore pointed out, the molten steel in the pool is in a turbulent condition and adapted to cause thorough mixing. The steel and lead thus mixed, it should be observed, enters the molds in an upwardly direction and moves outwardly toward the mold wall from its point of entry into the mold. This upward and outward action is opposite to the action which occurs during the normal gravity settling to top pouring practice and is highly desirable in aiding more thorough dispersion of the already distributed lead. The relatively heavier lead is thus mixed not only in the pool of steel at' the bottom of the center runner but also in the sprues and in the molds. The flow pattern is opposite to the flow pattern in current methods wherein top pouring is practiced.

The method of the invention is adapted to employ certain lead compounds or lead alloys which can be added "ice runner .in communication with the entry means .in the mold, pouring molten steel into said runner at a rate sufiicient to form a pool of molten steel in the bottom of the runner, pouring lead into the center runner so that it drops into the molten steel pool, continuing to pour the molten steel into the runner to replenish the pool and contemporaneously continuing to pour lead into the pool until the mold is filled to a desired extent, and permitting the mixture to solidify in the mold.

2. A method of mixing lead with steel so that the lead will be retained in the steel in a dispersed condition which Outside Bore Diameter Coupons were also taken at these same positions, polished and examined under the microscope at lOOX and SOOX. Lead could not be identified at these magnifications. Further, the transverse ingot slices were heated to 1l00 to 1300, held at this temperature for asuflicient time, but no lead segregation could be seen.

While there has been hereinbefore described an approved method of practicing the invention herein, it will be understood that many and various changes and modifications in the practice of the method may be made without departing from the spirit of the invention, and that all such changes and modifications as fall within the scope of the appended claims are contemplated as a part of this invention.

What we claim is:

l. A method of mixing lead with steel so that the lead will be retained in the steel in a dispersed condition which comprises providing a mold having means in its bottom portion to permit the entry of molten material to fill the mold upwardly, providing a substantially vertical comprises providing a mold having an opening in its bottom portion ;to permit the flow of molten material into the mold in an upward direction, providing a substantially vertical runner and a lateral sprue to establish communication between said runner and the mold opening, pouring molten steel into the center runner at a rate sufiicient to form a pool at the bottom of said runner While said runner is supplying the sprue with molten steel, pouring lead into the center runner so that it drops into the pool of molten steel, continuing to pour molten steel into the runner to replenish the pool and contemporaneously continuing to pour lead into the pool until the mold is filled to a desired extent, and permitting the mixture to solidify in the mold.

3. A method, according to claim 2, in which the lead poured into the center runner is in the form of pellets.

4. A method of mixing lead with steel so that the lead will be retained 'in the steel in a dispersed condition which comprises providing a plurality of molds each having .an entrance opening in its bottom portion to permit the flow of molten material into the mold in an upward direction, providing a substantially vertical runner having lateral sprues establishing communication between the vertical runner and the mold entrance openings, pouring molten steel into the center runner at a rate sufiicient to .form a turbulent pool at the bottom of said runner while said runner is supplying the sprues with molten steel, pouring lead into the center runner so that it drops into the turbulent pool of molten steel to be mixed therewith, continuing to pour molten steel into the runner to replenish the pool, contemporaneously continuing to pour lead into the pool until the mold is filled to a desired extent, and permitting the mixture to solidify in the mold.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A METHOD OF MIXING LEAD WITH STEEL SO THAT THE LEAD WILL BE RETAINED IN THE STEEL IN A DISPERSED CONDITION WHICH COMPRISES PROVIDING A MOLD HAVING MEANS IN ITS BOTTOM PORTION TO PERMIT THE ENTRY OF MOLTEN MATERIAL TO FILL THE MOLD UPWARDLY, PROVIDING A SUBSTANTIALLY VERTICAL RUNNER IN COMMUNICATION WITH THE ENTRY MEANS IN THE MOLD, POURING MOLTEN STEEL INTO SAID RUNNER AT A RATE SUFFICIENT TO FORM A POOL OF MOLTEN STEEL IN THE BOTTOM 